Study finds variation within species plays critical role in health of ecosystems

Concerns about biodiversity tend to focus on the loss of species, but a new study suggests that the loss of variation within species can also have important and unexpected consequences on the environment.

Many species play important roles in nature and provide services important to people. For example, many fish species are harvested for food, and many insect species pollinate wild and cultivated plants. The loss of these species may mean the loss of ecosystem services, which is a major motivation for preventing species extinctions.

Yet, a new study published Dec. 4 in Nature Ecology & Evolution found that the ecological effects of variations within species may be far reaching and often rival those of the entire species themselves.

"When we think of how human activities are impacting biodiversity, we are used to the idea that we're causing the extinction of a whole species," said Nash Turley, a postdoctoral research associate at the University of Central Florida and a co- author of the study. "But what we haven't thought about so much is the impact of losing biodiversity within a species. We barely know what variations within species are being lost. The times we have studied it, we see there are a lot more variations of species being lost than whole species. Our findings should make us second guess the idea that it's safe to ignore the variation seen within species."

Variation within species affects how organisms interact with each other and their surrounding environment. For example, the size of a fish's mouth, known as its gape, varies and determines the size of prey it can eat. Much of the time, traits like fish gape are adaptive; they help organisms live in a changing world. However, much less is known about how variation within species affects broader ecosystems.

This study, which was led by Simone Des Roches from UC Santa Cruz, examined all available studies that compared the ecological effects of variation within species to the effects of species presence (removing the species or replacing it with another). The 25 studies measured a total of 144 different ecological responses from various types of plants, animals and fungi. Their results show that variation within species, such as the effects of large- and small-gaped fish populations on zooplankton, are often similar to-and can sometimes be stronger than–whole species effects.

On average, species tend to have larger effects on ecosystems. Yet over a third of studies examined showed that swapping different variants of the same species had similar ecological effects as removing that species entirely or replacing it with a completely different species. And nearly half of all the studies evaluated documented at least one ecological response that was more strongly affected by variation within species than by a species' presence.

"Traditionally, ecologists have focused on the ecological importance of biodiversity among species. This paper broadly establishes within-species biodiversity as critical for ecology," said Eric Palkovacs, an associate professor of ecology and evolutionary biology at UC Santa Cruz and co-author of the paper.

The study suggests that protecting trait variation within species is not only important for the future of evolution, but also potentially critical for the functioning of current and future ecosystems.

"It's troubling because it suggests that human activities that impact diversity within species could cause ecological issues long before species go extinct," Turley said.

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Turley joined UCF in 2017 where he continues his research and teaches ecology classes. He has a Ph.D. in ecology and evolutionary biology from the University of Toronto, Canada. He was previously at Michigan State University and has published 15 academic articles since 2011 in addition to presenting at several national and international conferences.

In addition to Turley, Des Roches and Palkovacs, the co-authors of the paper include David Post at Yale University; Joseph Bailey and Jennifer Schweitzer at the University of Tennessee; Andrew Hendry at McGill University; and Michael Kinnison at the University of Maine. This work was funded by the Quebec Centre for Biodiversity, the UC Institute for the Study of Ecological and Evolutionary Climate Impacts, the David and Lucile Packard Foundation, and the National Science Foundation.